ESR studies of the binding of oxygen cobalt(II) bleomycin, nitric oxide iron(II) bleomycin and iron(III) bleomycin on oriented fibers of salmon sperm DNA have shown in each case that the sixth, axial ligand and/or in the in-plane ligands interact with other ESR experiments showing that these metallobleomycins are located at specific cleavage sequences, such results suggest that the metal domain regions of all of these cobalt and iron bleomycin species bind similarly to specific cleavage sites.